// 设置画布

const canvas = document.querySelector('canvas');
const ctx = canvas.getContext('2d');

const width = canvas.width = window.innerWidth;
const height = canvas.height = window.innerHeight;

// 生成随机数的函数

function random(min, max) {
    return Math.floor(Math.random() * (max - min)) + min
}

function randomColor() {
    return 'rgb(' +
        random(0, 255) + ', ' +
        random(0, 255) + ', ' +
        random(0, 255) + ')';
}


function Ball(x, y, velX, velY, color, size) {
    this.x = x;
    this.y = y;
    this.velX = velX;
    this.velY = velY;
    this.color = color;
    this.size = size;
}

Ball.prototype.draw = function () {
    ctx.beginPath();
    ctx.fillStyle = this.color;
    ctx.arc(this.x, this.y, this.size, 0, 2 * Math.PI);
    ctx.fill();

}

Ball.prototype.update = function () {
    if((this.x+this.size) >= width){
        this.velX = -(this.velX)
    }

    if ((this.x - this.size) <= 0){
        this.velX = -(this.velX)
    }

    if((this.y+this.size) >= height){
        this.velY = -(this.velY)
    }

    if ((this.y - this.size) <= 0){
        this.velY = -(this.velY)
    }

    this.x += this.velX;
    this.y += this.velY;
}

Ball.prototype.collisionDetect = function(){
    for (let j = 0;j<balls.length;j++){
        if (this !==balls[j]){
            const dx = this.x -balls[j].x;
            const dy = this.y - balls[j].y;
            const distance = Math.sqrt(dx * dx +dy * dy );

            if (distance < this.size + balls[j].size) {
                balls[j].color = this.color = randomColor();
            }
        }
    }
}

let balls = [];
while (balls.length<100) {
    let size = random(10,20);
    let ball = new Ball(
        random(0 + size,width - size),
        random(0 + size,width - size),
        random(-7,7),
        random(-7,7),
        randomColor(),
        size
    );
    balls.push(ball)
}

function loop() {
    ctx.fillStyle = 'rgba(0,0,0,0.25)';
    ctx.fillRect(0,0,width,height);

    for (let i = 0;i<balls.length;i++){
        balls[i].draw();
        balls[i].update();
        balls[i].collisionDetect();
    }
    requestAnimationFrame(loop);

}

loop();
